Rotating electric machine with permanent magnets and magnetic resistance having an improved structure

ABSTRACT

The invention concerns a rotating electric machine comprising a stator equipped with armature coils and a rotor mounted rotating inside the stator. The rotor having a rotor part with permanent magnet(s) and a rotor part with magnetic resistance. The rotor is substantially uniform over its axial surface and ahs along its tangential direction a distribution of polar parts with permanent magnet(s) each defining two poles of polarities imposed by magnet(s), ad polar parts with magnetic resistance each defining two poles with free polarities. The invention is applicable to motor vehicle alternators or AC starters.

BACKGROUND OF THE INVENTION

The present invention relates generally to rotating electrical machinesand in particular to a synchronous rotating machine having a permanentmagnet rotor.

The document “Comparison of different synchronous motor drives for fluxweakening applications”, N. Bianchi et al., proceedings of theInternational Conference on Electrical Machines (ICEM), Istanbul,Turkey, September 1998, volume ⅔, pages 946 et seq, and in particularFIG. 5 of the document and the associated description, discloses amachine whose rotor is separated into two coaxial parts disposedend-to-end in the axial direction.

A first part of the rotor constitutes an excitation magnet rotor and theother part constitutes a variable reluctance rotor.

Although a machine of the above kind has beneficial properties, inparticular in terms of flux weakening if the machine has to operateunder reduced load conditions, a major drawback is that it is necessaryto provide two types of yoke for rotor structure, i.e. a yoke for thepermanent magnet part of the rotor and a yoke for the variablereluctance part of the rotor.

A first object of the present invention is to alleviate this drawbackand to provide a rotor operating in accordance with the same principleusing a single yoke.

To be more precise, the present invention proposes to combine the tworotor parts into a single rotor whose yoke can therefore be made with asingle lamination shape.

BRIEF SUMMARY OF THE INVENTION

The present invention therefore proposes a rotary electrical machine, inparticular an alternator or combined alternator/starter motor forautomobile vehicles, comprising a stator equipped with stator windingsand a rotor mounted to rotate inside the stator, the rotor having apermanent magnet rotor part and a variable reluctance rotor part,characterized in that the rotor is substantially uniform throughout itsaxial length and has in its tangential direction a distribution ofpermanent magnet pole parts each defining two poles whose polarity isimposed by magnet(s) and variable reluctance pole parts each definingtwo poles whose polarity is not imposed.

Preferred, but non-limiting, features of the rotating machine accordingto the present invention are as follows:

the machine has the same number of permanent magnet pole parts andvariable reluctance pole parts, disposed alternately.

the machine has different numbers of permanent magnet pole parts andvariable reluctance pole parts, with at least one succession of at leasttwo pole parts of the same type.

each permanent magnet pole part comprises two magnets whose flux isessentially radial and which are disposed in the vicinity of theperiphery of the rotor.

the magnets are on the surface.

the magnets are buried.

the poles of the rotor are defined by interleaved pole claws of tworotor parts.

each permanent magnet pole part comprises a magnet whose flux isessentially tangential disposed in a notch formed between two regions ofsaid pole part which define its poles.

the permanent magnet pole parts and the variable reluctance pole partsare portions of a single yoke.

each variable reluctance pole part has arrangements for channelingmagnetic flux between its two poles.

each variable reluctance pole part has at least one buried auxiliarymagnet for channeling magnetic flux.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, aims and advantages of the present invention will becomemore apparent after reading the following detailed description ofvarious embodiments of the invention, which description is given by wayof non-limiting example and with reference to the accompanyingdiagrammatic drawings, in which:

FIG. 1 is a view in cross section of a first embodiment of a rotatingmachine according to the invention,

FIG. 2 is a view in cross section of a second embodiment of a rotatingmachine according to the invention,

FIG. 3 is a view in cross section of a third embodiment of a rotatingmachine according to the invention, and

FIG. 4 is a perspective view of the rotor of a second embodiment of arotating machine according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a rotating machine which comprises an annular externalstator 10 of conventional construction and whose yoke 12 defines aplurality of notches 14 delimited two by two by teeth 16 forming poles.The notches 14 accommodate single-phase stator windings 18. A multiphasestator with distributed windings and with or without shortening of thewinding pitch is equally feasible, of course.

The rotor 20 is preferably laminated and comprises permanent magnetsectors alternating in the circumferential direction with variablereluctance sectors. The sectors are preferably made from the samelaminations forming a common yoke 200.

In this embodiment, the rotor comprises permanent magnet sectors 210alternating with variable reluctance sectors 220 and each sector definestwo poles of the rotor. To be more precise, each sector 210 shown inFIG. 1 has a yoke part 212 and two magnets 214 a, 214 b of oppositepolarity mounted on the peripheral surface of the rotor. The two magnetstherefore define in the sector concerned a south magnetic pole PSA and anorth magnetic pole PNA.

Each sector 220 also has a yoke part 222 which defines a peripheralnotch 224 which is left empty in order to define two variable reluctancepoles PR1 and PR2. Two curved slots 226 and 228 extend alongside eachother to define a preferred trajectory for a magnetic field in eitherdirection between the poles PR1 and PR2.

Thin buried auxiliary magnets (not shown) can also be incorporated intothe sectors 220 to channel the flux and in particular to assist and toroute the magnetic flux generated by the permanent magnet sectorswithout degrading flux weakening behavior.

The sectors 210 and 220 are separated two by two by deep voids ornotches 230 extending from the periphery of the rotor and joining at thelevel of a central core 240 of the yoke 200 through which substantiallyno flux can pass.

The sectors 210 and 220 therefore alternate at the periphery of therotor to define on that periphery successive pairs of magnet poles PNAand PSA whose polarity is imposed by said magnets and pairs of variablereluctance poles PR1 and PR2 whose polarity is not fixed.

In particular, if the machine is operating under normal operatingconditions, the rotor comprises a succession of alternately south andnorth poles, namely a south pole PSA, a north pole PNA, a pole PR1 whichis a south pole because of the propagation of the magnetic flux in thesector 220, a pole PR2 which is a north pole for the same reason, and soon.

In contrast, if the machine is operating under flux weakeningconditions, because the current leads the back-EMF (this is a standardphenomenon), the sectors 220 allow the magnetic field to propagate inthe opposite direction, which corresponds to a succession of polescomprising a south pole PSA, a north pole PNA, a north pole PR1, a southpole PR2 and so on.

A combined permanent magnet/variable reluctance machine is thereforeobtained whose rotor has a homogeneous structure throughout its axiallength.

In a variant embodiment, not shown, the magnets 214 a, 214 b in eachsector 210 can be buried a predetermined small distance below theperipheral surface of the rotor.

FIG. 2 shows a rotating machine similar to that shown in FIG. 1 but inwhich the permanent magnet sectors are modified so that their south andnorth poles are produced by a single tangential flux magnet 215.

FIG. 2 shows that each sector 210 has a central notch 211 delimited bytwo yoke parts 213 a and 213 b and that a magnet 215 is housed in saidnotch 211 to define a south pole PSA at the level of the part 213 a anda north pole PNA at the level of the part 213 b.

Otherwise, this machine is identical to that shown in FIG. 1. Note thatthis embodiment obtains the benefit of the same operating principle withhalf the number of magnets.

FIG. 3 combines the embodiment of FIGS. 1 and 2 with an alternation ofsectors comprising a magnet sector 210 as shown in FIG. 1, a variablereluctance sector 220, a magnet sector 210 as shown in FIG. 2, avariable reluctance sector 220, and so on.

FIG. 4 shows an embodiment of the invention using a claw-pole rotor.

A claw-pole rotor conventionally comprises a first part 202 a with aparticular number of generally triangular pole claws 204 a and a secondpart 202 b with a particular number of generally triangular pole claws204 b. The pole claws 204 a, 204 b are interleaved with each other.

Thus in the circumferential direction of the rotor there are twovariable reluctance pole claws GR1 and GR2, two permanent magnet poleclaws GAS and GAN which have surface-mounted or buried magnets 214 a and214 b to impose respective south and north poles on them, and so on.

A rotor of this kind can include an excitation winding or not.

Of course, the present invention is in no way limited to the embodimentsdescribed and shown, to which the skilled person can apply any variantor modification conforming to the spirit of the invention.

In particular, depending on the required flux weakening capacity, therelative proportions of the permanent magnet pole sectors and thevariable reluctance pole sectors can be modified, for example to providea sector with permanent magnet south and north poles, a second identicalsector with permanent magnet south and north poles, a sector with twovariable reluctance poles, then another two sectors each with twopermanent magnet poles, and so on.

Compared to the machine described in the article referred to in theintroduction, this corresponds to some extent to modifying thedistribution between the axial lengths of the permanent magnet rotorpart and the variable reluctance rotor part of the prior art machine.

The present invention applies in particular to alternators and combinedalternator/starter motors for automobile vehicles.

What is claimed is:
 1. A rotary electrical machine, in particular an alternator or combined alternator/starter motor for automobile vehicles, comprising a stator equipped with stator windings and a rotor mounted to rotate inside the stator, the rotor having a permanent magnet rotor part and a variable reluctance rotor part, wherein the rotor is substantially uniform throughout its axial length and has in its tangential direction a distribution of permanent magnet pole parts with a permanent magnet(s) each defining two poles whose polarity is imposed by the magnet(s) and variable reluctance pole parts each defining two poles whose polarity is not imposed.
 2. A machine according to claim 1, wherein it has the same number of permanent magnet pole parts and variable reluctance pole parts, disposed alternately.
 3. A machine according to claim 2, wherein each permanent magnet pole part comprises two magnets whose flux is essentially radial and which are disposed in the vicinity of the periphery of the rotor.
 4. A machine according to claim 2, wherein each permanent magnet pole part comprises a magnet whose flux is essentially tangential disposed in a notch formed between two regions of said pole part which define its poles.
 5. A machine according to claim 1, wherein it has different numbers of permanent magnet pole parts and variable reluctance pole parts, with least one succession of at least two pole parts of the same type.
 6. A machine according to claim 5, wherein each permanent magnet pole part comprises two magnets whose flux is essentially radial and which are disposed in the vicinity of he periphery of the rotor.
 7. A machine according to claim 5, wherein each permanent magnet pole part comprises a magnet whose flux is essentially tangential disposed in a notch formed between two regions of said pole part which define its poles.
 8. A machine according to claim 1, wherein each permanent magnet pole part comprises two magnets whose flux is essentially radial and which are disposed in the vicinity of the periphery of the rotor.
 9. A machine according to claim 8, wherein the magnets are on the surface.
 10. A machine according to claim 9, wherein the poles of the rotor are defined by interleaved pole claws of two rotor parts.
 11. A machine according to claim 8, wherein the magnets are buried.
 12. A machine according to claim 11, wherein the poles of the rotor are defined by interleaved pole claws of two rotor parts.
 13. A machine according to claim 11, wherein the permanent magnet pole parts and the variable reluctance pole parts are portions of a single yoke.
 14. A machine according to claim 8, wherein the poles of the rotor are defined by interleaved pole claws of two rotor parts.
 15. A machine according to claim 1, wherein each permanent magnet pole part comprises a magnet whose flux is essentially tangential disposed in a notch formed between two regions of said pole part which define its poles.
 16. A machine according to claim 15, wherein the permanent magnet pole parts and the variable reluctance pole parts are portions of a single yoke.
 17. A machine according to claim 1, wherein the permanent magnet pole parts and the variable reluctance pole parts are portions of a single yoke.
 18. A machine according to claim 17, wherein each variable reluctance pole part has arrangements for channeling magnetic flux between its two poles.
 19. A machine according to claim 1, wherein each variable reluctance pole part has arrangements for channeling magnetic flux between its two poles.
 20. A machine according to claim 19, wherein each variable reluctance pole part has at least one buried auxiliary magnet for channeling magnetic flux.
 21. A machine according to claim 1, wherein each variable reluctance pole part has at least one buried auxiliary magnet for channeling magnetic flux. 